Acetabular cup prosthesis component for total or subtotal hip prosthesis system

ABSTRACT

An acetabular cup prosthesis assembly for total or subtotal hip replacement, including a metallic, unitary cup member having a dome portion defining a socket larger than the head of the femur or femoral prosthesis component to be accommodated, and including an integral flange rim to seat against the acetabulum and be secured thereto by screws. The cup has sharp edged fins to be seated in the acetabulum and restraining ribs on the interior surface of the socket. A replaceable plastic liner insert of hemispheric configuration interfits in the socket and has grooves shaped to provide a snap fit with the restraining ribs.

[ 1 Sept. 9, 1975 I ACETABULAR CUP PROSTHESIS COMPONENT FOR TOTAL ORSUBTOTAL HIP PROSTHESIS SYSTEM [76] Inventor: William Minor Deyerle,2222 Monument Ave., Richmond, Va, 23220 [22] Filed: June 12, I974 [21]Appl, No; 478,732

{S21 U.S. Cl. 3/1912; 128/92 C [5]] Int. C1. 4. A6IF 1/24 [58] Field ofSearch 3/1, 1.9-1912;

128/92 C, 92 CA, 92 R OTHER PUBLICATIONS Vila/Hum Surgical Appliances(catalog), Austenal C0.

New York, NY, 1974, McBride Acetabulum Cups," No. 6429 on p, 3Ov

Primary Examiner-Ronald L. Frinks Attorney, Agent, or FirmMas0n, Fenwick& Lawrence 1 1 ABSTRACT An acetabular cup prosthesis assembly for totalor subtotal hip replacement, including a metallic, unitary cup memberhaving a dome portion defining a socket larger than the head of thefemur or femoral prosthe sis component to be accommodated, and includingan integral flange rim to seat against the acetabulum and be securedthereto by screws. The cup has sharp edged fins to be seated in theacetabulum and restraining ribs on the interior surface of the socket. Areplaceable plastic liner insert of hemispheric configuration interfitsin the socket and has grooves shaped to provide a snap fit with therestraining ribs.

16 Claims, 7 Drawing Figures ACETABULAR CUP PROSTHESIS COMPONENT FORTOTAL OR SUBTOTAL HIP PROSTl-IESIS SYSTEM BACKGROUND AND OBJECTS OF THEINVENTION The present invention relates in general to prosthetic devicesfor use in total and subtotal hip replacements, and more particularly toan acetabular cup assembly which may be implanted on the acetabulum tocorrect hip problems, usable with or without a femoral prosthesiscomponent.

Heretofore, total hip prosthesis surgery has been performed wherein acup is fitted in the acetabulum and a head or femoral prosthesis member,which comprises a stem or shank portion and an artificial head, is fixedto the femur to provide a prosthetic hip joint. Also, to relieve certainconditions, particularly in young patients where there is no immediateneed for amputating the head of the femur and substituting a femoralprosthesis member, subtotal hip replacement surgery such as a cuparthorplasty may be performed where a cup is implanted in the acetabulumor cupshaped socket in the pelvis. In either case, the acetabulum cup orcup prosthesis component provides a socket for receiving the head of thefemur or the head of the femur prosthesis component.

Heretofore, metal acetabulum cups have been employed, for example, forprotrusio-acetabuli and in rheumatoid arthritic cases, or in performingtotal hip prosthesis surgery, wherein the cup provides a metal surfacedsocket for receiving the head of the femur or the head of the femoralprosthesis component, providing either a bone to metal or a metal tometal contact in the hip socket. While methyl methacrylate bone cementhas been previously used for fixation of the acetabular cup used in theprior art in the recipient pelvis, this bone cement may present aserious hazard to the patient, as pointed out in the recent article byEdith R. Kedes, M.D., et al entitled Inoperative Deaths Associated WithAcrylic Bone Cement", Journal American Medical Association, Vol. 222,No. 5, pp. 575-577, Oct. 30, 1972. Furthermore, improved acetabular cupfixation means is desired, as methyl methacrylate is notorious for itsbrittleness and lack of resistance to shear. Also, if it becomesnecessary to replace the acetabular cup prosthesis at any time in thefuture, fixation with methyl methacrylate may require badly chopping therecipient pelvis attempting to remove the methyl methacrylate.

I have found it desirable to provide a rimmed acetabular cup which maybe securely fixed in the recipient pelvis by the use of screws extendingthrough flanged portions of the rimmed cup into the acetabulum tosecurely fix the metal cup in position. The flanged rimmed cup givesmany options in the selection of the proper treatment in a specific hipproblem. In a young patient where it is thought that a cup arthroplastymay give the patient six to ten years of good function and postpone theneed for a total hip, the rimmed cup can be implanted. The femur headcan be reshaped and used in that situation until such time as the headand neck are absorbed. At that time a total hip can then be inserted inthe exact same position as the rimmed cup with less surgery and no stockis lost by the use of the rimmed cup for the cup arthroplasty. The cupshould be place between 30 and 45 verticle and l forward facing toprovide stability for the cup arthroplasty and later stability for thetotal hip.

Furthermore, I have found it desirable to provide a replaceable plasticliner for the concave socket formed by the acetabular cup prosthesis,formed of a high density monomer plastic insert that may be removed atseven to ten years or at any time that sufficient wear occurs andreplaced without removing the acetabular cup from the pelvis. Theconcave socket portion of the acetabular cup prosthesis is speciallyformed to receive and support the plastic liner or insert, and tofacilitate its removal and replacement when required. A furtheradvantage of the metal encased plastic liner is that this avoids theslight but definite tendency of a high density monomer to stretch ordrape, since the metal encasement formed by the body of the acetabularcup will give a more symmetrical support than would methyl methacrylatecement in which plastic acetabular cups have been heretofore embedded tofix it in the acetabulum.

An object of the present invention, therefore, is the provision of anovel flanged rimmed acetabular cup prosthesis formed of a metal bodydefining a socket for reception of the head of the femur or a femoralprosthesis component, which is fixed to the acetabulum by screwsextending into the recipient pelvis without use of methyl methacrylatebone cement and which has a replaceable plastic liner or insert whichcan be removed and replaced from the acetabular cup without removingeither the femoral component or the metallic component of the acetabularcup. Even if methyl methacrylate or any other substance were used as afiller, my flanged rimmed cup would still stabilize and prevent movementof the cup.

Other objects, advantages and capabilities of the present invention willbecome apparent from the following detailed description, taken inconjunction with the accompanying drawings illustrating the preferredembodiment of the invention.

BRIEF DESCRIPTION OF THE FIGURES FIG. I is an exploded perspective viewof an acetabular cup prosthesis assembly embodying the presentinvention;

FIG. 2 is a front or bottom view of the cup component of the assembly;

FIG. 3 is a side elevation of the cup component;

FIG. 4 is a rear or top view of the cup component;

FIG. 5 is a section view through the cup and insert components of theassembly, taken from the section plane of line 5-5 of FIG. 2;

FIG. 6 is a rear or top view of the insert or liner of the assembly; and

FIG. 7 is a side elevation of the insert.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The acetabular cupprosthesis component assembly of the present invention is indicatedgenerally by the reference character 10 and comprises a rimmed metalacetabular cup 12 illustrated best in FIGS. 1 and 2, and a replaceablehigh density plastic liner or insert 14 removably assembled with therimmed metal acetabular cup. The rimmed metal cup component 12 is asolid unitary, integral cast structure comprising a dome shaped bodyportion I6 forming a socket for reception of the head of the femur orthe head of the femoral prosthesis component, such, for example, as thatde scribed and illustrated in my earlier U.S. patent application Ser.No. 183,418, now US. Pat No. 3,814,089, the dome shaped body 16 havingan interior concave, generally spherical surface 18 and an exteriorconvex, generally spherical surface 20 both formed about a commoncenter. The metal cup 12 forms a generally spherical socket 22 forreception of the head of the femur or of the femoral prosthesis,surrounded or bounded at the entrance opening to the socket 22 by anannular rim or rim flange 24 which in the preferred embodiment has anincident or lower surface 24a facing towards the femur or femoralprosthesis component which lies in an upwardly flaring or upwardlydiverging truncated conical path as will be apparent from FIG. 3. Theupper or posterior surface 24b of the annular rim portion 24, relativeto the femur, may lie in a plane perpendicular to the center line oraxis of the dome por tion intercepting the zenith of the dome, or it mayalso be in an upwardly and outwardly diverging conical path, as desired.In the preferred form herein illustrated, three reinforcing flanges orwebs are provided at positions faced 90 apart extending from theexterior convex spherical surface 20 of the dome portion 16 to the outeredge of the rim portion 24, having a truncated crescent shaped lateralprofile, forming reinforcing web flanges 26 strengthening the domeportion and further fixing the position of the rim portions relativethereto. Also in the illustrated embodiment, three pairs of holes 28 areprovided in the rim at positions spaced circumferentially approximately90 apart, for reception of fixation screws 30 to be inserted in thedrill holes in the acetabulum to fix the cup 12 in position.

The interior concave spherical surface 18 of the dome portion 16 isinterrupted by a plurality of inwardly projecting arcuate lugs or ridges32, of rectangular cross section, which in the illustrated embodimentare in cruciate or cruciform configuration alined with a pair ofdiametric bisectors of the dome disposed at right angles to each otherand forming meridian rib segments extending from the socket entrance toan'intersection at the zenith of surface 18.

The replaceable plastic liner or insert 14, best shown in FIGS. 5 and 6,is also a generally dome shaped body 36 having a spherically concaveinner surface 38 whose center of revolution is in the plane of the loweror anterior face 40 of the insert, and includes a spherically convexouter surface 42 having its center of revolution spaced upwardly orposteriorly of the plane of the incident or anterior surface 40, as willbe apparent from inspection of FIG. 7. The spherically convex outersurface 42 is shaped and sized to conform to the interior concavespherical surface 18 of the dome shaped body portion 16 of the cup, andis provided with arcuate slots or kerfs 44, of cruciate configuration inthe illustrated embodiment, conforming in configuration precisely to thecruciate lugs or ridges 32 of the cup, and having, if desired, a slight45 chamfer or bevel formation along all of the exterior edges of theslots. The insert or liner 14 is made of an ultra high molecular weightpolyethylene or similar high density plastic material or other suitablematerial and is designed to be received by a snap fit in the socket 22formed by the dome portion 16 of the cup 12.

To prepare the acetabulum and install the acetabular cup assembly of thepresent invention, the acetabulum is exposed by known surgicalprocedures, and the approximate location of the acetabular cupprosthesis site and the position to be assumed by the cup is preferablydetermined by using a Kuntschner nail, for example, a 10 or 12 mm. nailwhich is held parallel with the anterior iliac crests and a 45 angleflag is slipped on to form a guide for placing the cup. The cup is to beplaced between 45 and 30. A 30 angle flag is also tested and by trialinsertion of the cup prosthesis, the amount of reaming necessary can bedetermined. In some cases of large acetobuli or protrusio'acetabuli itis only neces sary to remove the cartilage lining of the acetabuli withlittle reaming of the bone.

Before the acetabulum is reamed, one is careful to leave between aquarter and a half inch of the lateral cartilagenous margin of theacetabulum intact, and to assist in this marks this portion with anosteotome. In some cases there is no cartilage in which case the hardbone is left intact. Using an osteotome and a gauge, the medial wall andthe medial two-thirds of the acetabulum are denuded of all cartilagedown to bleeding bone with an osteotome before any reaming. This tendsto displace the cup as far medially as possible and still maintainsufficient medial wall support to avoid fracture into the pelvis. Again,the angle to be assumed by the cup is checked with the 45 measurementflag inserted on the Kuntschner nail held alined with the anterior iliaccrests, and a cup reamer of the exact size of the exterior convexspherical surface 20 of the dome is applied to ream the dome shapedsocket in the acetab ulum to receive the cup body 12. The cup prosthesisis preferably disposed so that it is faced downwardly be tween 30 and 45with forward facing of 10 which is the normal forward facing of theaverage acetabulum. After the acetabulum is reamed with the dome shapedcup reamer to a point where the edge of the reamer is about one-eighthinch under the rim of the acetabulum, a rim reamer is then inserted,which has a smooth 1-7/8 inches dome the exact size of the outer surface20 of the cup, and having reamer teeth on an annular portion outwardlysurrounding the smooth dome shaped portion. This rim reamer does notream anywhere except in the rim region, and is employed to ream a recessthe exact size to receive the annular rim portion 24 of the cupprosthesis.

After the rim reamer has been used, the cup prosthesis 12 is reinsertedwith the three reinforcing flanges or webs 26 positioned anterior andposterior and absent on the medial side. Using a nylon insertim impactorhaving a 15/8 inch nylon domeshaped head for impacting the metal cup,the cup prosthesis 12 is tamped lightly to mark a place within theacetabulum for the three flanges 26. Frequently a Cutting is requiredfor the superior and inferior flange, and occasionally for the lateralflange. The lateral flange is not usually sunk into the edge of theacetabulum.

Throughout the reaming procedure, the lateral onehalf or one-fourth inchcartilage rim or hard bone is still left in place, tending to force thecutting medially as the reamer will not cut as well on the cartilage ason the denuded bone. This also preserves a good lateral lip displacingthe cup medially. The cup is firmly seated, with the impactor, usingseveral hammer blows, after the sites for the three reinforcing flangesor webs 26 have been cut as required, to firmly seat the cup in theacetabulum, drill holes are then drilled in the acetabulum to receivethe mounting screws, and two or three chrome cobalt molibidum screws orscrews of other acceptable material are inserted into the drill holes.These screws have an average length of l-A inches. All of the anteriorand lateral holes are carefully checked for depth by a depth gauge aswell as palpating with the finger within the pelvis, as extreme cautionmust be taken to avoid penetrating the pelvis in the region of thesciatic notch. The two or three fixation screws 30 through selected onesof the holes 28 serve the purpose of maintaining the position of the cupafter it has been well impacted. After 8 to 10 weeks, the rim andflanges provide the main stabilizing effect. The advantage of screws notbeing over 2 inches long is that the plasticity of the pelvis is muchgreater than the plasticity of the metal and or acrylic which may beburied in it, thus minimizing the length of dissimilar material relativeto longer screw lengths and reducing the potential motion between them.

In one satisfactory example, the rimmed metal acetabular cup had amaximum diameter of about 2.43 inches at the outer periphery of the rim24, the dome shaped portion 16 had a height from the posterior or uppersurface 24b of the rim to the zenith or peak of the dome of about 0.837inch, the distance from the zenith of the dome to the plane of theentrance to the socket was about 1.085 inches, and the thickness of therim at its outer periphery was about 0.090 inch. The interior concavespherical surface 18 of the socket 22 was sized to exactly conform toand accept the exterior surface 42 of the insert 14, which in apreferred embodiment had a spherical radius of about 0.875 inch. Theradius of the inner spherical surface 38 of the insert in the preferredembodiment was about 0.55 inch, or a diameter of about 1.105, and theradium of the bottom of the kerfs or slots 44 was about 0.77 inch.

With the removable plastic liner 14 in the dome portion of the cup 12,the cup assembly accepts a 28 mm. head on a femur prosthesis component.The liner 14 is held in position by the cruciate lugs or ridges 32 thatare snapped immovably into position in the conforming kerfs or slots 44in the insert when the insert is installed in the cup using a nylonimpactor having a 28 mm. nylon head. The initial cup when installed inthe acetabulum is usually installed in one piece with the liner alreadyinserted. This offers the option of replacement of the liner after anyperiod of time when wear becomes significant. To replace the liner, thehip is merely dislocated and using an oscillating saw and osteotome, twocross cuts are made along the diametric planes of the ribs into theremaining liner to cut the liner into four pieces for ease of removalfrom the cup 12 without having to cut through the full thickness of theliner portions intervening between the rib segments. A removable newplastic liner of similar construction and configuration may then beinserted with a nylon impacter.

If desired, an annular washer may be alined with one of the screw holes28 in the annular rim overlying the outer surface thereof through whichone of the fixation screws is inserted, the washer being of sufficientdiameter so that an edge portion thereof outwardly overlaps the edge ofthe flat lower face 40 of the insert to bear tightly against the face 40and provide added insurance against motion. The real fixation of theplastic liner, however, is secured by the self locking cruciateconformation of the cup and plastic liner. The liner will not move inthe metal cup due to the fact that the friction at the periphery will begreater than the friction in the center portion with the 28 mm.prosthesis head.

Of course, if there is any difficulty in removing the liner from thecup, by removing the fixation screws in the holes 28 of the annular rim24, the entire cup can be removed and replaced with a new plastic liner.It is highly advantageous to be able to offer the patient the option ofa new liner, which is made available by the construction of the presentinvention, when the liner of the existing installation becomes eithermechanically unstable or causes symptoms from debris or products fromthe wearing of the plastic in the head and socket region. By theconstruction of the invention, the old liner can be replaced by a newliner to avoid these difflculties without the necessity of replacing theentire hip and without the necessity of massive surgery to extricatecups which have been seated and fixed with methyl methacrylate assometimes practiced in the prior art.

What is claimed is:

1. An acetabular cup prosthesis assembly to be fixed on the acetabulumof a patient in connection with total or sub total hip prosthesissurgery, comprising an integral unitary metal cup prosthesis componentand a replaceable liner insert, the cup prosthesis component having adome portion extending in a hemispherical path from a proximal end planeof the prosthesis formed of a substantially hemispherical metal wallhaving a convex spherical outer surface and a concave spherical innersurface defining a generally hemispherical cup socket having an entranceopening at said proximal end plane and having a diameter ofpredetermined greater size than the head of an associated femur orfemoral prosthesis component to be located in said cup socket, said cupprosthesis component also including an annular rim flange extendingradially outwardly from the end of said hemispherical metal wall at saidproximal end plane defining an integral annular ring portion encirclingsaid entrance opening to abut against surface portions of a recipientacetabulum and be secured thereto to locate and aid in supporting thecup prosthesis thereon, said dome portion including rotation and tiltingresisting and liner retaining rib formations protruding radiallyinwardly from said spherical inner surface, said rib formations beingformed of a pair of semicurclar ribs spanning the cup socket alongmeridians disposed in a pair of diametric planes intersecting at thezenith of the inner surface of said wall defining patterns of meridianrib segments extending from the entrance opening to the zenithintersection to present surfaces to the liner resisting tilting androtation thereof in the socket and for frictionally retaining the linerseated in the socket. and the replaceable liner insert being formed ofan integral molded body ofplastic material ofgencrally hemisphericalconfiguration interfitted in said cup socket having an outer sphericalsur face conforming closely to the size and complementing theconfiguration of the inner spherical surface and meridian rib segmentsof the dome portion to restrain the liner insert in said cup socket bytight frictional interengagcment therewith. and said liner insert havinga concave spherical inner surface defining a liner socket of a diametercorresponding to the heads of the femur or femoral prosthesis to belocated therein.

2. An acetabular cup prosthesis assembly as defined in claim 1, whereinsaid diametric planes of the semicircular meridian ribs are located atright angles to each other whereby said meridian rib segments define acruciate pattern.

3. An acetabular cup prosthesis assembly as defined in claim 2, whereinsaid meridian rib segments are continuous uninterrupted ribs of uniformheight and thickness throughout their extent from said entrance open ingto the zenith of the inner surface of said wall, the ribs therebydefining diametric planes along which the liner may be cut, subdividingthe liner into four quad rants for ease of removal from the socketwithout having to cut through the full thickness of the liner portionsintervening between rib segments.

4. An acetabular cup prosthesis assembly as defined in claim 1, whereinfin formations of truncated crescent configuration in profile arelocated in quadrature relation about the outer surface of thehemispherical wall with the truncated end edges of the fin formationsintegrally joined to said annular rim flange and extending outwardlyfrom said wall to the outer periphery of said annular rim flange. theouter edges of the fin formations extending along outwardly convex arcsand merging into said convex spherical outer surface of said walladjacent the zenith thereof.

5. An acetabular cup prosthesis assembly as defined in claim 1 whereinsaid meridian rib segments are continuous uninterrupted ribs of uniformrectangular cross section throughout and of uniform height and thicknessthroughout their extent from said entrance opening to the zenith of theinner surface of said wall, the ribs thereby defining diametric planesalong which the liner may be cut, subdividing the liner into fourquadrants for ease of removal from the socket without having to cutthrough the full thickness of the liner portions intervening betweensaid rib segments and said outer spherical surface of said liner inserthaving grooves therein of uniform rectangular cross section closelyconforming to the cross section and configuration of said meridian ribsegments to receive the latter in tightly interfitted relation therein.

6. An acetabular cup prosthesis assembly as defined in claim 1, whereinsaid dome portion includes a plurality of circumferentially spaced,outwardly extending fin formations projecting from the outer concavesurface thereof and having sharp outer edges extending in diametricplanes of the hemisphere defined by said metal wall to be forced intothe bone structure of the acetabulum at plural locations surrounding thedome portion.

7. An acetabular cup prosthesis assembly as defined in claim 1, whereinthe outer spherical surface of said liner insert includes grooves formedtherein precisely conforming to said inwardly extending elongated ribson the inner surface of said wall and shaped to provide a snap fittherewith frictionally restraining the insert in the cup socket.

8. An acetabular cup prosthesis assembly as defined in claim 2, whereinthe outer spherical surface of said liner insert includes grooves formedtherein precisely conforming to said inwardly extending elongated ribson the inner surface of said wall and shaped to provide a snap fittherewith frictionally restraining the insert in the cup socket 9. Anacetabular cup prosthesis assembly as defined in claim 3, wherein theouter spherical surface of said liner insert includes grooves formedtherein precisely conforming to said inwardly extending elongated ribson the inner surface of said wall and shaped to provide a snap fittherewith frictionally restraining the insert in the cup socket.

10. An acetabular cup prosthesis assembly as defined in claim 1, whereinsaid liner insert has an incident annular planar face spaced outwardly aslight distance from said proximal end plane surrounding an entranceopening for said liner socket, said spherical inner surface of saidinsert having its center in the plane of said planar face and said outerspherical surface of said insert having its center spaced toward thezenith of said cup socket from said planar face.

11. An acetabular cup prosthesis assembly as defined in claim 3, whereinsaid liner insert has an incident an nular planar face spaced outwardlya slight distance from said proximal end plane surrounding an entranceopening for said liner socket, and the spherical inner surface of saidinsert having its center in the plane of said planar face and said outerspherical surface of said insert having its center spaced toward thezenith of said cup socket from said planar face.

12. An acetabular cup prosthesis assembly as defined in claim 4, whereinsaid liner insert has an incident annular planar face spaced outwardly aslight distance from said proximal end plane surrounding an entranceopening for said liner socket, said spherical inner surface of saidinsert having its center in the plane of said planar face and said outerspherical surface of said insert having its center spaced toward thezenith of said cup socket from said planar face.

13. An acetabular cup prosthesis assembly as defined in claim 7, whereinsaid liner insert has an incident annular planar face spaced outwardly aslight distance from said proximal end plane surrounding an entranceopening for said inner socket, said spherical liner surface of saidinsert having its center in the plane of said planar face and said outerspherical surface of said insert having its center speced toward thezenith of said cup socket from said planar face.

14. An acetabular cup prosthesis assembly as defined in claim 1, whereinsaid cup prosthesis has a plurality of screw holes solely located insaid annular rim flange in a circumferential path spaced radiallyoutwardly from the periphery of said liner for receiving fixation screwsto extend into the recipient acetabulum of the patient for fixation ofthe cup prosthesis component thereon.

15. An acetabular cup prosthesis assembly as defined in claim 3, whereinsaid cup prosthesis has a plurality of screw holes solely located insaid annular rim flange in a circumferential path spaced radiallyoutwardly from the periphery of said liner for receiving fixation screwsto extend into the recipient acetabulum of the patient for fixation ofthe cup prosthesis component thereon,

16. An acetabular cup prosthesis assembly as defined in claim 7, whereinsaid cup prosthesis has a plurality of screw holes solely located insaid annular rim flange in a circumferential path spaced radiallyoutwardly from the periphery of said liner for receiving fixation screwsto extend into the recipient acetabulum of the patient for fixation ofthe cup prosthesis component thereon.

1. An acetabular cup prosthesis assembly to be fixed on the acetabulumof a patient in connection with total or sub-total hip prosthesissurgery, comprising an integral unitary metal cup prosthesis componentand a replaceable liner insert, the cup prosthesis component having adome portion extending in a hemispherical path from a proximal end planeof the prosthesis formed of a substantially hemispherical metal wallhaving a convex spherical outer surface and a concave spherical innersurface defining a generally hemispherical cup socket having an entranceopening at said proximal end plane and having a diameter ofpredetermined greater size than the head of an associated femur orfemoral prosthesis component to be located in said cup socket, said cupprosthesis component also including an annular rim flange extendingradially outwardly from the end of said hemispherical metal wall at saidproximal end plane defining an integral annular ring portion encirclingsaid entrance opening to abut against surface portions of a recipientacetabulum and be secured thereto to locate and aid in supporting thecup prosthesis thereon, said dome portion including rotation and tiltingresisting and liner retaining rib formations protruding radiallyinwardly from said spherical inner surface, said rib formations beingformed of a pair of semicurclar ribs spanning the cup socket alongmeridians disposed in a pair of diametric planes intersecting at thezenith of the inner surface of said wall defining patterns of meridianrib segments extending from the entrance opening to the zenithintersection to present surfaces to the liner resisting tilting androtation thereof in the socket and for frictionally retaining the linerseated in the socket, and the replaceable liner insert being formed ofan integral molded body of plastic material of generally hemisphericalconfiguration interfitted in said cup socket having an outer sphericalsurface conforming closely to the size and complementing theconfiguration of the inner spherical surface and meridian rib segmentsof the dome portion to restrain the liner insert in said cup socket bytight frictional interengagement therewith, and said liner insert havinga concave spherical inner surface defining a liner socket of a diametercorresponding to the heads of the femur or femoral prosthesis to belocated therein.
 2. An acetabular cup prosthesis assembly as defined inclaim 1, wherein said diametric planes of the semicircular meridian ribsare located at right angles to each other whereby said meridian ribsegments define a cruciate pattern.
 3. An acetabular cup prosthesisassembly as defined in claim 2, wherein said meridian rib segments arecontinuous uninterrupted ribs of uniform height and thickness throughouttheir extent from said entrance opening to the zenith of the innersurface of said wall, the ribs thereby defining diametric planes alongwhich the liner may be cut, subdividing the liner into four quadrantsfor ease of removal from the socket without having to cut through thefull thickness of the liner portions intervening between rib segments.4. An acetabular cup prosthesis assembly as defined in claim 1, whereinfin formations of truncated crescent configuration in profile arelocated in quadrature relation about the outer surface of thehemispherical wall with the truncated end edges of the fin formationsintegrally joined to said annular rim flange and extending outwardlyfrom said wall to the outer periphery of said annular rim flange, theouter edges of the fin formations extending along outwardly convex arcsand merging into said convex spherical outer surface of said walladjacent the zenith thereof.
 5. An acetabular cup prosthesis assembly asdefined in claim 1 wherein said meridian rib segments are continuousuninterrupted ribs of uniform rectangular cross section throughout andof uniform height and thickness throughout their extent from saidentrance opening to the zenith of the inner surface of said wall, theribs thereby defining diametric planes along which the liner may be cut,subdividing the liner into four quadrants for ease of removal from thesocket without having to cut through the full thickness of the linerportions intervening between said rib segments and said outer sphericalsurface of said liner iNsert having grooves therein of uniformrectangular cross section closely conforming to the cross section andconfiguration of said meridian rib segments to receive the latter intightly interfitted relation therein.
 6. An acetabular cup prosthesisassembly as defined in claim 1, wherein said dome portion includes aplurality of circumferentially spaced, outwardly extending finformations projecting from the outer concave surface thereof and havingsharp outer edges extending in diametric planes of the hemispheredefined by said metal wall to be forced into the bone structure of theacetabulum at plural locations surrounding the dome portion.
 7. Anacetabular cup prosthesis assembly as defined in claim 1, wherein theouter spherical surface of said liner insert includes grooves formedtherein precisely conforming to said inwardly extending elongated ribson the inner surface of said wall and shaped to provide a snap fittherewith frictionally restraining the insert in the cup socket.
 8. Anacetabular cup prosthesis assembly as defined in claim 2, wherein theouter spherical surface of said liner insert includes grooves formedtherein precisely conforming to said inwardly extending elongated ribson the inner surface of said wall and shaped to provide a snap fittherewith frictionally restraining the insert in the cup socket.
 9. Anacetabular cup prosthesis assembly as defined in claim 3, wherein theouter spherical surface of said liner insert includes grooves fomredtherein precisely conforming to said inwardly extending elongated ribson the inner surface of said wall and shaped to provide a snap fittherewith frictionally restraining the insert in the cup socket.
 10. Anacetabular cup prosthesis assembly as defined in claim 1, wherein saidliner insert has an incident annular planar face spaced outwardly aslight distance from said proximal end plane surrounding an entranceopening for said liner socket, said spherical inner surface of saidinsert having its center in the plane of said planar face and said outerspherical surface of said insert having its center spaced toward thezenith of said cup socket from said planar face.
 11. An acetabular cupprosthesis assembly as defined in claim 3, wherein said liner insert hasan incident annular planar face spaced outwardly a slight distance fromsaid proximal end plane surrounding an entrance opening for said linersocket, and the spherical inner surface of said insert having its centerin the plane of said planar face and said outer spherical surface ofsaid insert having its center spaced toward the zenith of said cupsocket from said planar face.
 12. An acetabular cup prosthesis assemblyas defined in claim 4, wherein said liner insert has an incident annularplanar face spaced outwardly a slight distance from said proximal endplane surrounding an entrance opening for said liner socket, saidspherical inner surface of said insert having its center in the plane ofsaid planar face and said outer spherical surface of said insert havingits center spaced toward the zenith of said cup socket from said planarface.
 13. An acetabular cup prosthesis assembly as defined in claim 7,wherein said liner insert has an incident annular planar face spacedoutwardly a slight distance from said proximal end plane surrounding anentrance opening for said inner socket, said spherical liner surface ofsaid insert having its center in the plane of said planar face and saidouter spherical surface of said insert having its center speced towardthe zenith of said cup socket from said planar face.
 14. An acetabularcup prosthesis assembly as defined in claim 1, wherein said cupprosthesis has a plurality of screw holes solely located in said annularrim flange in a circumferential path spaced radially outwardly from theperiphery of said liner for receiving fixation screws to extend into therecipient acetabulum of the patient for fixation of the cup prosthesiscomponent thereon.
 15. An acetabular cup prosthEsis assembly as definedin claim 3, wherein said cup prosthesis has a plurality of screw holessolely located in said annular rim flange in a circumferential pathspaced radially outwardly from the periphery of said liner for receivingfixation screws to extend into the recipient acetabulum of the patientfor fixation of the cup prosthesis component thereon.
 16. An acetabularcup prosthesis assembly as defined in claim 7, wherein said cupprosthesis has a plurality of screw holes solely located in said annularrim flange in a circumferential path spaced radially outwardly from theperiphery of said liner for receiving fixation screws to extend into therecipient acetabulum of the patient for fixation of the cup prosthesiscomponent thereon.